Semiconductor dies typically include an active area having circuits formed therein. After fabrication of circuits on a semiconductor die, detection of faults is often desirable. Detecting these faults without destroying the circuitry on the semiconductor is also useful. Because the circuits were preserved during fault detection, the circuits can also undergo other non-destructive testing prior to deprocessing. Once the position of the fault is detected and other testing completed, the circuits may be deprocessed in order to determine the exact nature of the fault or to farther investigate the properties of the circuit.
Conventional semiconductor dies are mounted on a substrate to form semiconductor packages. In conventional packages, the die is mounted with the active area up, away from the substrate. In flip-chip packages, the die is mounted with the active area down, in proximity to the substrate. In either case, it is desirable to detect faults in the circuits in the active area.
Certain faults in the circuits, such as shorts, generate heat. In order to detect faults which cause hot spots, liquid crystals are conventionally used. For a conventional package, a thin layer of liquid crystal is poured over the circuits at the top of the die. For a flip-chip package, the back of the die is thinned, then a thin layer of liquid crystal is poured over the surface of the back of the die. Power is then provided to the circuits on the die. The liquid crystal changes phase over any hot spots in the circuits. Consequently, the liquid crystal appears to change color over these hot spots in the circuit. Alternatively, the liquid crystal moves away from the hot spots, leaving an exposed area of the die. These hot spots and, therefore, areas where the liquid crystal appears to have changed color mark the position of certain faults in the circuits. Consequently, the position of faults in the circuit can be detected.
Although conventional liquid crystal detection functions for circuits in conventional packages, the use of liquid crystal has several drawbacks. Liquid crystal is relatively expensive. Liquid crystal is also hazardous to the health of a user. In addition, the conventional method for using liquid crystal to detect faults may be relatively difficult to perform.
Accordingly, what is needed is a system and method for detecting faults in circuits on conventional packages and in particular flip-chip packages without destroying the circuits. The present invention addresses such a need.